Electric furnace having a heating element of carbon or graphite for producing temperatures under high pressures



p 24, 1968 SENNOSUKE SATO 3, 03,

ELECTRIC FURNACE HAVING A HEATING ELEMENT OF CARBON OR GRAPHITE FORPRODUCING TEMPERATURES v I I j UNDER HIGH PRESSURES Filed Sept. 14, 19652 Sheets-Sheet 1 INVENTOR Sept. 24, 1968 SENNOSUKE sATo 3,403,212

ELECTRIC FURNACE HAVING A HEATING ELEMENT OF CARBON OR GRAPHITE, FORPRODUCING TEMPERATURES Filed Sept. 14; 1965 UNDER HIGH PRESSURES 2Sheets-Sheet 2 1 qy J- Crap/lite 4 V L d f a Gas l l l 7mpera fave KINVENTOR BY I WQLMQLM United States Patent 3,403,212 ELECTRIC FURNACEHAVING A HEATING ELEMENT OF CARBON OR GRAPHITE FOR PRODUCINGTEMPERATURES UNDER HIGH PRESSURES Sennosuke Sato, Ibaragi-ken, Japan,assignor to Nihon Genshiryoku Kenkyusho, Tokyo, Japan, a corporation ofJapan Filed Sept. 14, 1965, Ser. No. 487,289 Claims priority,application Japan, Sept. 21, 1964, 39/ 53,572 2 Claims. (Cl. 13--31)ABSTRACT OF THE DISCLOSURE An electric furnace is provided and has ahollow carbon heating element core member, a furnace body including acasing enclosing the core member, and a heat insulation powdered carbonfilling the casing and surrounding the hollow core member. A sealedpressure vessel is received in the furnace body, power leads connect tothe core member, means supply the pressure vessel with an inert gas, andgas-permeable members of low density graphite are arranged close toinert gas introducing apertures formed in the casing.

This invention relates to electric furnaces of the resistance-heatingtype including a hollow core member of carbon or graphite as a heatingelement and has for its object to provide an electric furnace of thetype described which is capable of producing superhigh temperaturesunder high pressures with the entire furnace body accommodated in apressure vessel.

Electric resistance furnaces of the general type have an advantageousfeature that they can be temperature-controlled with ease, but, in orderto attain temperatures exceeding 3300 K., they are required to employ acore material which has sufficiently high softening and meltingtemperatures and is stable undergoing no chemical change in ahigh-temperature atmosphere. One metallic material satisfying thisrequirement is tungsten. Carbon or graphite is known to have asublimation temperature of 3620 K. under normal pressure but itspractical use is limited to the temperature range up to approximately3400 K. One previous form of graphite tube furnace is the one designedby the inventor and disclosed in the Journal of the Society of MaterialsScience Japan, vol. 14, No. 137, pp. 93-94 (February 1965).

Under these circumstances, in order to provide an electric resistancefurnace for producing superhigh temperatures it is a prerequisite toprevent softening and sublimation at such high temperatures of carbon orgraphite, forming the heating element of the furnace.

Carbon or graphite forming a heating element has a gas-liquid-solidphase at 4l00 K. if placed in an atmosphere pressurized to approximately100 atm. However, under pressures exceeding the critical pressure ofcarbon, though it has correspondingly higher melting and boiling points,its critical temperature in its solid-liquid phase has a value ofapproximately 4l00 K. irrespective of the pressure and no highertemperature is realizable. With regard to this, reference may be had tothe constitutional diagram (FIG. 3), which corresponds to the one onpage 118 of the book Nuclear Graphite by R. E. Nightingale, AcademicPress, 1961.

In practice, the highest usable temperature is also limited due to thenecessity of avoiding any softening of the furnace core or heatingelement. Experiments show, however, that the carbon or graphite core canwithstand even a temperature as high as approximately 4100 K., ifsubjected thereto only for a limited period of time, in con- 3,403,212Patented Sept. 24, 1968 trast to the normal working temperature of 3900K. or under.

According to the present invention, a satisfactory result can beobtained by employing a commercially available carbon powder or carbonblack as a heat-insulting material. Carbon powder is microscopically anelectrical or heat conductor but forms a D001 conductor as a mass ofpowder, forming a peerless heat insulator at superhigh temperatures ofthe order of 3900 K.

The electric furnace according to the present invention is utilizablefor melting and refining different metal and alloy materials as well asvarious ceramic materials at superhigh temperatures of up toapproximately 3900 K. and is also highly useful in measuring differentphysical, chemical and electrical qualities of such materials and intheir researches.

Further, according to the present invention, there is provided anelectric furnace for producing superhigh temperatures which is highlyhelpful in high-temperature analysis of refractories and heat-resistantmaterials, formation of artificial jewel crystals, and researches onhigh-temperature gases including plasmas.

According also to the present invention, there is provided an electricfurnace which can realize a wide range of superhigh temperatures withstableness and thus is highly valuable compared with conventionalfurnaces of the electric-arc or light-focusing type.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawing, in Which:

FIG. 1 is a longitudinal cross-sectional view of an electric furnaceembodying the present invention, taken along the line I-I in FIG. 2,with a portion of the furnace body shown in external appearance;

FIG. 2 is a cross-sectional view of same, taken along the line IIII inFIG. 1; and

FIG. 3 is a constitutional diagram of graphite showing its state varyingwith temperature and pressure.

Referring to FIGS, 1 and 2, reference numeral 1 indicates a hollowtubular core member formed of graphite which is energizable for heatgeneration by an electric current fed through conductors 18 to metallicterminals 2. The tubular core member 1 is enclosed in a metallic casing4 with end plates 3 of insulating material such as hard asbestos securedto the opposite ends of the casing. The casing 4, forming the furnacebody, is encircled with coiled cooling tubes 5. Cooling rings 6, 6 arearranged on the respective ends of the core member 1 and eachcommunicate with a water inlet pipe 60 and a water outlet pipe 20 forcirculation of cooling water through the cooling ring 6. Axially spacedspiders 7, formed of graphite, serve to support the core member 1 in thecasing 4 coaxially therewith by way of ceramic insulating shoes 8interposed between the inner wall of the casing and the adjacent ends ofthe respective spider legs. The tubular core member 1 is apertured tocommunicate with radially extending temperature-measuring tubes 9,through which radiant rays can be led from within the core memberexteriorly of the furnace.

Carbon powder 10 is loaded in the space in the casing 4 surrounding thetubular core member 1. Arranged at the opposite ends of the casing 4inside of the respective end plates 3 are gas-permeable rings 11, formedof lowdensity graphite, for the purpose of equalizing the inert gaspressures inside and outside of the casing 4. Each of the graphite rings11 is formed on its outer end surface with an annular groove 11a, whichis in communication with a plurality of through apertures 30 formed inthe adjacent end plate 3. Tubes 19 are connected to the hollow tubularcore member 1 at its opposite ends so that inert gas may be filledtherein through the tubes as indicated at a. As indicated at 0, insertgas is also filled in a pressure vessel 14, which accommodates thefurnace body, through an opening 15, connecting to a suitable pressuresource, formed in the bottom wall of the vessel, as indicated at c. Theinert gas is led into the heat-insulating material 10, loaded in thecasing 4, through the apertures 30 in the end plates 3, groove 11a inthe graphite rings 11 and through the gas-permeable texture thereof sothat the gas pressures inside and outside of the hollow core member 1are balanced with each other.

Reference numeral 12 indicates stays secured to the inner wall of thepressure vessel 14 to support the furnace body in place therein.Inert-gas preheating and directing members 13 of graphite are insertedin the hollow core member 1 at its opposite ends and are each externallyhelically grooved as at 13 so that the inert gas a fed through theadjacent pipe 19 into the core member 1 proceeds helically along thegroove 13 while being preheated by the heat of the core member itself.In this manner, it will be apparent that in the core member 1 isobtained a uniform pressure distribution of the inert gas.

The wall of the pressure vessel 14 is designed to withstand a pressureof 105 atm. or over depending upon the working temperature of thefurnace and is also designed to fully withstand not only the thermalstress caused by the differential temperature within the vessel but alsoany dynamic stresses such as the slow cyclic fatigue caused by therepetition of the thermal stress. The bottom opening 15 in the pressurevessel 14 is provided for introduction of electric conductors, coolingtubes, inert-gas supply and pressure-gage pipings, etc. into the furnacebody. End covers 16 are secured to the wall of the pressure vessel atits opposite ends by bolt means and can be removed for insertion of theobject to be heated into the hollow core member and its removaltherefrom. Reference numeral 17 indicates observation windows formed inthe wall 14 of the pressure vessel in alignment with thetemperature-measuring tubes 9 secured to the core member.

The following table includes various data obtained with one practicalembodiment of the present invention.

Core temperature, K.:

Working 3900.

Duration 100 hours (4100 K.).

Modifications of the structure herein disclosed may suggest themselvesto those skilled in the art, and it is to be understood that the presentdisclosure relates to a preferred embodiment of the present inventionwhich is by way of example only and is not to be narrowly construed.

What is claimed is:

1. An electric furnace of the resistance-heating type including a hollowcarbon heating element core member, a furnace body including a casingenclosing said hollow core member, a heat insulation of powdered carbonfilling said casing and surrounding said hollow core member for thelength thereof with an inert gas sealed in said casing for equalizingthe gas pressure inside and outside of said hollow core member, a heatresistant sealed pressure vessel receiving said furnace body therein,power supply leads connecting to said core member, means to supply saidpressure vessel with an inert gas under pressure, said core member beingdesigned to receive an object to be heated, said casing having aplurality of apertures for introducing inert gas into the interior ofsaid closed casing, and

gas-permeable members of low-density graphite arranged close to saidapertures and positioned in said casing.

2. An electric furnace of the resistance-heating type including a hollowcarbon heating element core member, a furnace body including a casingenclosing said hollow core member, a heat insulation of powdered carbonfilling said casing and surrounding said hollow core member for thelength thereof with an inert gas sealed in said casing for equalizingthe gas pressures inside and outside of said hollow core member, a heatresistant sealed pressure vessel receiving said furnace body therein,power supply leads connecting to said core member, means to supply saidpressure vessel with an inert gas under pressure, means connect to theends of said core member to supply the inert gas thereto and onlyrelease heated gas into said core member, and

graphite spiders engaging said core member intermediate the ends thereofto aid in positioning it in said casing.

References Cited UNITED STATES PATENTS 2,125,588 8/1938 Ridgway 13252,768,277 10/ 1956 Buck et al. 219-427 2,778,866 1/1957 Sanz et al. 132O3,150,226 9/1964 Thorne et al. 13-25 3,244,141 4/1966 Weech et al. 13-31X BERNARD A. GILHEANY, Primary Examiner.

VOLODYMYR Y. MAYEWSKY, Assistant Examiner,

